In the past, there has been a need to control sand or other solids produced from the formation with the flowing oil or other hydrocarbons. Techniques for sand control have involved the use of screens. Various configurations have been attempted for sand-control screens. These screens have generally involved a rigid base pipe which is perforated, overlaid by one or more layers of screen of different opening sizes. Generally, the finest screen, which is the one that is designed for catching the sand or other solid material, is a screen most prone to not only plugging but also other mechanical ailments.
In the past, these fine filtering screens have used very thin wire wrapped around the base pipe and an underlying coarser screen. The filtering screen has generally in the past had a welded longitudinal seam which failed generally due to erosive effects of the flow through the screen or chemical attack on the weldment. Sealing off the ends of the filtering screen to the underlying support structure has also been problematic. Again, due to the fine wire size of the filtering screen, welding the ends to a support body has resulted in failures due to differential expansion creating tensile loads on welds involving fine wire components of the filtering screen. Various mechanical efforts to seal the filtering screen to the underlying structure, such as by use of mechanical bands, has also failed to provide a tight seal, thereby allowing the hydrocarbons to short circuit around the filtering screen, carrying the undesirable sand with them.
In the past, underlying coarse screens below the sand-filtering screen have been made with a wound wire having a triangular cross-section, with a flat side oriented outwardly. This has resulted in coarse screens with fairly small open areas and created numerous dead spots behind the filtering screen where the flat side of the triangularly cross-section wound wire of the underlying coarser screen butted up against the openings of the finer sand-filtering screen. As a result, the sand-filtering screen suffered from losses of efficiency due to the numerous dead spots encountered by the outer flat side of the wound coarse screen broadly abutting the sand-filtering screen.
In order to address these problems encountered in prior sand-control screen systems, a method and apparatus have been developed to improve the performance of such screens. One of the objectives of the present invention is to provide a finished assembly that does not suffer from welded attachments to thin members, which had in the past been a weak point in resisting stress, particularly due to tensile loading, flow erosion, as well as chemical attack. Another object of the invention is to create a more efficient sand-control screen assembly by employing a substrate of a coarse screen, having wound wires of a more rounded or arcuate cross-section, to reduce the dead zones in between the filtering screen and the underlying coarse screen. Another object is to provide a simple mechanical technique for assembling the elements of the screen so that it will give efficient and longer lasting service than the prior designs. These and other objectives will be better understood by a review of the detailed description which follows below.